1. Field of the Invention
This present invention is related generally to control of spacecraft, and more particularly to control of propulsion and/or attitude of such spacecraft using microwave-electro-thermal (MET) thrusters.
2. Statement of the Prior Art
The invention described and claimed herein comprises an improved MET thruster and fuel therefor.
MET thrusters according to the present invention produce rocket thrust for the control of spacecraft via electricity for small satellites. A MET thruster produces high-temperature rocket exhaust by sending microwaves into a resonant cavity where an excited mode then creates an electrodeless discharge that heats gaseous or liquid fuel.
One drawback in MET thrusters according to prior approaches has been their use of a microwave power coupling, between the microwave generator and the resonant cavity and plasma, which typically consists of a rigid waveguide with impedance matching equipment. Such waveguides and their associated impedance matching hardware, however, greatly adds to the weight and size of the propulsion system, making it impractical for spaceflight. In particular, the size of the system and rigid waveguide connections make it difficult to place the MET thrust chamber on a steerable gimbaled platform on the spacecraft.
Another drawback in MET thrusters according to prior approaches has been their proposed use of fuels (e.g., hydrogen, helium, ammonia, and hydrazine) which are either highly toxic, flammable, irritating or difficult to store. This has limited the usefulness of the MET, making any proposed launching of satellites propelled by MET thrusters from the cargo bay of the space shuttle very expensive due to precautions and tests needed to ensure the safety of the shuttle crew in case of fuel leaks. The processing and testing of proposed ME-equipped satellites to be launched on ordinary boosters was also complicated and made more expensive by the presence of dangerous fuels carried for the MET thruster.
The foregoing problems are overcome, and other advantages are provided by not only greatly reducing or eliminating the waveguide and impedance matching equipment, but also providing a safe, non-toxic fuel for the MET thruster.